1. Towards System Architecture for Tiny Networked Devices Jason Hill http://www.cs.berkeley.edu/~jhill http://www.cs.berkeley.edu/~jhill/tos U.C. Berkeley 6/20/2000

2. Endeavor Retreat2 An End-to-end Perspective Desktops –max out at few 100M –in your face –connected to the infrastructure Ubiquitous Devices –billions –sensors / actuators –PDAs / smartphones / PCs –heterogeneous Service Path Scalable Infrastructure –highly available –persistent state (safe) –databases, agents –service programming environment

3. 6/20/2000Endeavor Retreat3 Key Characteristics of TNDs Small physical size and low power consumption Concurrency-intensive operation –flow-thru, not wait-command-respond Limited Physical Parallelism and Controller Hierarchy –primitive direct-to-device interface Diversity in Design and Usage –application specific, not general purpose –huge device variation => efficient modularity => migration across HW/SW boundary Robust Operation –numerous, unattended, critical => narrow interfaces

4. 6/20/2000Endeavor Retreat4 Mote Initial Platform 4Mhz, 8bit MCU 512 bytes RAM, 8K ROM 900Mhz Radio 10-30 ft. range Temperature Sensor Light Sensor LED outputs Serial Port

5. 6/20/2000Endeavor Retreat5 Tiny OS Scheduler and Graph of Components –constrained two-level scheduling model: threads + events Component: –Frame (storage) –Threads (concurrency) –Commands, and Handlers (events) Constrained Storage Model –frame per component, shared stack, no heap Very lean multithreading Layering –components issue commands to lower-level components –event signal high-level events, or call lower-level commands »Guarantees no cycles in call chain

6. 6/20/2000Endeavor Retreat6 TOS Component Messaging Component init Power(mode) TX_packet(buf) TX_packet _done (success) RX_packet_ done (buffer) Internal State init power(mode) send_msg(ad dr, type, data) msg_rec(type, data) msg_send_ done (success) send_msg_thread /* Messaging Component Declaration */ //ACCEPTS: char TOS_COMMAND(AM_SEND_MSG)(char addr,char type, char* data); void TOS_COMMAND(AM_POWER)(char mode); char TOS_COMMAND(AM_INIT)(); //SIGNALS: char AM_MSG_REC(char type, char* data); char AM_MSG_SEND_DONE(char success); //HANDLES: char AM_TX_PACKET_DONE(char success); char AM_RX_PACKET_DONE(char* packet); //USES: char TOS_COMMAND(AM_SUB_TX_PACKET)(char* data); void TOS_COMMAND(AM_SUB_POWER)(char mode); char TOS_COMMAND(AM_SUB_INIT)();

7. 6/20/2000Endeavor Retreat7 Composition RFM Radio byte Radio Packet UART Serial Packet i2c Temp photo Active Messages clocks bit byte packet Route map routersensor appln application HW SW

8. 6/20/2000Endeavor Retreat8 Programming with CAD Can assemble overall system using structural VHDL Scripts pre-process VHDL at compile time Allows for compile time resolution of event handlers –Eliminates need for registration mechanisms and dynamic dispatch Automatically allows events to be handled by multiple components. (TX_Done) Significantly more flexibility than library based component models

9. 6/20/2000Endeavor Retreat9 Migration of the Hardware Software Boundary TinyOS component model propagates hardware abstractions into software Allows for a migrations of software components into hardware: Example: –Bit level radio procession component could be implemented as specialized FIFO with complex pattern matching.

10. 6/20/2000Endeavor Retreat10 Dynamics of Events and Threads Message Send Transition Timing diagram of event propagation

11. 6/20/2000Endeavor Retreat11 Empirical Breakdown of Effort can take apart time, power, space, … 50 cycle thread overhead, 10 cycle event overhead Components Packet reception work breakdown Percent CPU UtilizationEnergy (nj/Bit) AM 0.05%0.20%0.33 Packet 1.12%0.51%7.58 Ratio handler 26.87%12.16%182.38 Radio decode thread 5.48%2.48%37.2 RFM 66.48%30.08%451.17 Radio Reception --1350 Idle-54.75%- Total 100.00% 2028.66

12. 6/20/2000Endeavor Retreat12 Storage Breakdown (C Code) 3450 B code 226 B data

13. 6/20/2000Endeavor Retreat13 Projects this Term Device Proxy Architecture –mobile-IP RDP variant Integration with infrastructure –JINI and Ninja Multithreaded vs. federated architecture Pluggable adaptive MAC layer –often periodic, moment of crisis –sleep cycling Ad Hoc routing component Connectivity-based location detection smart badge + sensor in smart space

14. 6/20/2000Endeavor Retreat14 Multi-Hop Routing Demo Sensors automatically detect routing topology Base station broadcasts out routing information Individuals listen for an propagate route update –N messages sent Generational scheme to prevent cycles in routing table Base

15. 6/20/2000Endeavor Retreat15 Multi-Hop Routing Demo (cont.) Sensor information propagated up routing tree Statistics kept as to number of readings received and number of packets forwarded for each node Sensors transmit data when significant events occur or when time limit is exceeded Must be continuously listening for packets to be forwarded

16. 6/20/2000Endeavor Retreat16 Second generation hardware design is under way Mote designed for experimentation Additional Sensors –2 Axis Accelerometer and 2 Axis Magnetometers »Allows dead reckoning in 2-D plane –Humidity, Temperature, and Pressure sensor –Transmission strength sensor and control Expansion capabilities through external BUS –The hardware sandwich Ability to directly plug into logic analyzer for debugging purposes

17. 6/20/2000Endeavor Retreat17 Current and Future Work Quantify error characteristics of RFM Radio –Allows selection of coding techniques that optimize throughput and reliability Aggressive inlining to minimize overhead of modules Document and release code for others to use Determine limitations of TinyOS Incorporate more exciting HW architectures Integrate with Ninja active proxies and Base services